In a motor apparatus, when supplying a motor with alternating current transformed by an inverter from direct current generated by a direct current power supply, there is a technique that transforms the voltage of the direct current with a transformer circuit located in a stage preceding the inverter. The transformer circuit includes switches and inductors. Such a system requires switches and inductors that are highly costly and large in size. Patent document 1 discloses a motor apparatus that includes a battery connected to a neutral point of stator coils and performs step-up control. The motor apparatus opens the switch located between the battery and the neutral point when there is an abnormality.